For battery packs in mobile devices, radios, etc., a discharge blocking circuit is a necessary feature for batteries with exposed rear charging-interface terminals. The discharge blocking circuit is configured to inhibit the presence of cell voltage from appearing across the rear terminals as well as to improve battery charging efficiency by eliminating heat dissipation and reducing voltage drop from the charger to the battery pack's cells. The discharge blocking circuit is further coupled to the battery pack's Thermistor terminal. A presence of potential difference at the rear charging-interface terminals, when exposed to ionic/conductive vapor, can accelerate the corrosion process (by electrolysis), such as when subjected to salt fog test conditions. As consumer demand for lighter radio increases, magnesium alloy, known for its lightweight properties, is being introduced, replacing its heavier predecessor, aluminum alloy, as the base material for a radio chassis. In a typical radio construction, a battery is firmly attached to the radio rear chassis. The rear charging-interface terminals of batteries are made of nickel alloy material for low surface resistance, while the radio rear chassis is of magnesium alloy. The anodic index for magnesium alloy is −1.75V, whereas the anodic index for nickel alloy is −0.35V. When both metals are electrically connected via an electrolyte, a potential difference of 1.4V forms at the nickel alloy terminals with respect to the magnesium alloy chassis.
In conventional discharge blocking circuit designs, a voltage as low as 0.5V on a thermistor rear charging-interface terminal, is sufficient to disable the discharge blocking feature, hence presenting the full cell voltage appearing across the positive charge (CH+) and negative charge (CH−) terminals, which further latches the thermistor line to high, facilitating a strong electrolysis process in an ionic/salt solution accelerating corrosion on one of the terminals. To merely change the triggering threshold from 0.5V to higher voltages, in conventional discharge blocking circuits, will inhibit the functionality of the discharge blocking circuit when at high temperatures, due to lower impedance of the thermistor (negative temperature coefficient (NTC) device) when hot. To relocate the triggering rear charging-interface terminal, for the discharge blocking circuit, in this case the thermistor rear charging-interface terminal, away from the magnesium alloy chassis has been futile as well as impacting battery miniaturization, charger pocket design and the like.
Accordingly, there is a need for an efficient apparatus and method for inhibiting corrosion with discharge blocking features in a battery.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.